Page 38 - Nanotechnology an introduction

Chapter Contents

4.1 The “Physical” Nano/Bio Interface55
4.1.1 Organisms 56
4.1.2 Tissues 56
4.1.3 Cells 57
Penetration of Nano-Objects into the Cell's Interior 57
The Response of a Cell to External Nanostructured Features 58
Eukaryotic Cells 59
Prokaryotic Cells 61
4.1.4 Biomolecules 62
4.2 Nanomedicine64
4.2.1 A Concept System for Nanomedicine 64
4.2.2 Wider Implications 68
4.3 Nanotoxicology68
4.4 Summary70
4.5 Further Reading71
The nano/bio interface means: (1) the “living proof of principle” that nanoscale mechanisms (the subcellular molecular machinery inside a living cell) exist and can function; (2) the man–machine interface aspect: how humans control atomic-
scale assembly, and how atomic-scale assembly is scaled up to provide artifacts of human dimensions; (3) the physical boundary between a living organism and a nanomaterial, device or system. This “bio-physical” interface has several
characteristic scales from the biological viewpoint: organismal, cellular and biomolecular. Each scale is examined, considering the nano/bio as a special case of the general problem of the bio–nonbio (living–nonliving) interface. As a very
important manifestation of nanobiotechnology, nanomedicine is defined and discussed, concluding with the toxicology of nano-objects.
Keywords: cells, biomolecules, nanomedicine, biomedical surfaces, nanotoxicology
As nanotechnology becomes more widely written and talked about, the term “nano/bio interface”, as well as several variants such as the “nano–bio”
and “bio–nano interfaces”, have emerged. This chapter gives an extended definition of what the nano/bio interface is and what it might involve.
One of nanotechnology's protagonists, Eric Drexler, has robustly countered scepticism that Feynman's concept of making machines that make
smaller machines could be continued down to the atomic level (Section 1.3) by adducing the many examples of biological mechanisms operating
at the nanoscale [43]. This biological “living proof-of-principle” has since been vastly reinforced by the acquisition of ever more detailed knowledge
of the mechanisms of these biological machines. This “living proof-of-principle” may be considered as a virtual nano/bio interface.

Apart from this rather abstract meaning, the nano/bio interface clearly must signify the interface between a nanostructured nonliving domain and the
living domain. It therefore constitutes a special case of the nonliving/living interface, in which the scale of salient features on the nonliving side is
constrained to fall within a certain range. Nothing is, however, specified regarding the scale of the living side. This could be the very largest scale,
that of an entire ecosystem or of society. Below that, it might be useful to consider (multicellular) organisms, organs, tissues, cells and molecules.
Clearly very different phenomena enter at each scale.

Let us consider the distinction between information flowing from the nano domain to the bio domain and vice versa. These two sitiations are
denoted respectively as the nano–bio and bio–nano interfaces. The meanings of the two can be quite different. For example, considering the
interface between nanotechnology and society, the nano–bio interface denotes the impact nanotechnology has on society; for example, how it
might be completely transformed by the advent of molecular manufacturing. Conversely, the bio–nano interface denotes the introduction of
regulatory measures for nanotechnology. Considering the general environment, the nano–bio interface implies, for example, the response of soil
microbes to nanoparticles added for remediation purposes; and conversely the bio–nano interface implies the destruction of nanoparticles added
for remediation purposes by soil microbes. At the scale of an organism (e.g., a human being), the nano–bio interface signifies the technology of
scaling atomic-scale assembly up or out to provide human-sized artifacts; conversely the bio–nano interface corresponds to the man–machine
interface, which a human being would use to control a nanoscale assembly process. Insofar as digitally encoded control is likely to be used, there
should be no difference in principle between the interface for controlling a nanoscale process and one for controlling a macroscale process.

Feynman [56] mentions Albert R. Hibbs's suggestion of a miniature “mechanical surgeon” (nowadays referred to as a nanoscale robot or nanobot)
able to circulate within the bloodstream and carry out repairs in situ. Hogg [77] conceives such a device as being about the size of a bacterium,
namely a few hundred nanometers in diameter. The nano/bio interface is literally (physically) delineated by the outer surfaces of the device and its
nanoscale appendages; that is, the zone between the device and its living host. More generally, this meaning of the nano/bio interface refers to any
situation in which a nanomaterial or a nanodevice is in contact with living matter.
If the radius of the “bio” side of the interface is less than that of the “nano” side (Figure 4.1), we can refer to bio–nano; conversely if the radius of the
“nano” side of the interface is less than that of the “bio” side, we can refer to nano–bio.

Figure 4.1 Left hand: a sharply curved “finger” of a protein abuts an inorganic surface. Right hand: a sharply curved inorganic nanoparticle abuts a living cell membrane.
A further meaning of “nano/bio interface” is the means with which humans interact with a nanodevice. While the protagonists of nanobots typically
envisage a fully autonomous device, appraising its surroundings, processing the information internally and carrying out appropriate tasks
accordingly, Hibbs presumed that information about its surroundings would be transmitted to a human surgeon, who upon analyzing the data would